U.S. patent application number 15/169878 was filed with the patent office on 2016-12-15 for composite for anode active material, anode including the composite, lithium secondary battery including the anode, and method of preparing the composite.
The applicant listed for this patent is Samsung Electronics Co., Ltd., Samsung SDI Co., Ltd.. Invention is credited to Seongho Jeon, Byoungsun Lee, Jaemyung Lee, Kanghee Lee, Hosang Park.
Application Number | 20160365569 15/169878 |
Document ID | / |
Family ID | 57516041 |
Filed Date | 2016-12-15 |
United States Patent
Application |
20160365569 |
Kind Code |
A1 |
Lee; Jaemyung ; et
al. |
December 15, 2016 |
COMPOSITE FOR ANODE ACTIVE MATERIAL, ANODE INCLUDING THE COMPOSITE,
LITHIUM SECONDARY BATTERY INCLUDING THE ANODE, AND METHOD OF
PREPARING THE COMPOSITE
Abstract
A composite anode active material, the composite including: a
metal particle; a carbon-containing material, and a garnet-type
lithium ion conductor, wherein an amount of the garnet-type lithium
ion conductor is greater than 1 part by weight and less than 5
parts by weight, based on 100 parts by weight of a total weight of
the metal particle, the carbon-containing material, and the
garnet-type lithium ion conductor.
Inventors: |
Lee; Jaemyung; (Seoul,
KR) ; Jeon; Seongho; (Yongin-si, KR) ; Park;
Hosang; (Seoul, KR) ; Lee; Byoungsun; (Seoul,
KR) ; Lee; Kanghee; (Suwon-si, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Samsung Electronics Co., Ltd.
Samsung SDI Co., Ltd. |
Suwon-si
Yongin-si |
|
KR
KR |
|
|
Family ID: |
57516041 |
Appl. No.: |
15/169878 |
Filed: |
June 1, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 4/38 20130101; H01M
4/485 20130101; H01M 4/364 20130101; H01M 2004/027 20130101; H01M
4/625 20130101; Y02E 60/10 20130101; H01M 10/0525 20130101 |
International
Class: |
H01M 4/36 20060101
H01M004/36; H01M 10/0525 20060101 H01M010/0525; H01M 4/38 20060101
H01M004/38; H01M 4/62 20060101 H01M004/62; H01M 4/485 20060101
H01M004/485 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 9, 2015 |
KR |
10-2015-0081503 |
Claims
1. A composite anode active material, the composite comprising: a
metal particle; a carbon-containing material; and a garnet-type
lithium ion conductor, wherein an amount of the garnet-type lithium
ion conductor is greater than 1 part by weight and less than 5
parts by weight, based on 100 parts by weight of a total weight of
the metal particle, the carbon-containing material, and the
garnet-type lithium ion conductor.
2. The composite of claim 1, wherein the metal particle comprises
silicon, tin, germanium, aluminum, a combination thereof, or an
alloy thereof.
3. The composite of claim 1, wherein the carbon containing material
comprises a carbon nanotube, a carbon nanofiber, graphene,
graphite, or a combination thereof.
4. The composite of claim 1, wherein the garnet-type lithium ion
conductor comprises a garnet-type oxide represented by Formula 1A:
L.sub.5+xE.sub.3Me.sub.zM.sub.2-zX.sub.d Formula 1A wherein, in
Formula 1A, L is a monovalent cation, a divalent cation, or a
combination thereof and comprises lithium, E is a trivalent cation,
Me and M are each independently a trivalent cation, a tetravalent
cation, a pentavalent cation, or a hexavalent cation, X comprises
O, a pentavalent anion, a hexavalent anion, a heptavalent anion, or
a combination thereof, and 0<x.ltoreq.3, 0.ltoreq.z<2, and
0<d.ltoreq.2.
5. The composite of claim 4, wherein L in Formula 1A comprises
lithium, sodium, magnesium, calcium, potassium, hydrogen, or a
combination thereof.
6. The composite of claim 4, wherein Me in Formula 1A comprises a
transition metal.
7. The composite of claim 4, wherein Me in Formula 1A comprises
tantalum, niobium, yttrium, scandium, tungsten, molybdenum,
antimony, bismuth, hafnium, vanadium, germanium, silicon, aluminum,
gallium, titanium, cobalt, indium, zinc, chromium, or a combination
thereof.
8. The composite of claim 1, wherein the garnet-type lithium ion
conductor has an ionic conductivity of at least about
3.0.times.10.sup.-4 siemens per centimeter at a temperature of
25.degree. C.
9. The composite of claim 1, wherein an amount of the metal
particle is in a range of about 10 parts by weight to about 90
parts by weight, based on 100 parts by weight of the
carbon-containing material.
10. The composite of claim 1, wherein the garnet-type lithium ion
conductor comprises a garnet-type oxide represented by
L.sub.5+xE.sub.3-aQ.sub.aMe.sub.zM.sub.2-zX.sub.d Formula 1B
wherein, in Formula 1B, L is a monovalent cation, a divalent
cation, or a combination thereof and comprises lithium, E is a
trivalent cation, Q is a Group 1 element having an atomic weight of
at least 10, Me and M are each independently a trivalent cation, a
tetravalent cation, a pentavalent cation, or a hexavalent cation, X
comprises O, a pentavalent anion, a hexavalent anion, a heptavalent
anion, or a combination thereof, 0<x.ltoreq.3, 0.ltoreq.z<2,
0<d.ltoreq.2, and 0<a.ltoreq.3.
11. The composite of claim 10, wherein an amount of the Group 1
element having an atomic weight of at least 10 is in a range of
about 0.25 part by weight to about 3.85 parts by weight, based on
100 parts of weight of a total amount of the garnet-type lithium
ion conductor.
12. The composite of claim 11, wherein the Group 1 element having
an atomic weight of at least 10 is present at a grain boundary of
the garnet-type oxide of Formula 1B.
13. The composite of claim 1, wherein the garnet-type lithium ion
conductor comprises a garnet-type oxide represented by Formula 2:
L.sub.5+x+2yD.sub.yE.sub.3-yMe.sub.zM.sub.2-zX.sub.d Formula 2
wherein, in Formula 2, L is a monovalent cation, a divalent cation,
or a combination thereof and comprises Li, D is a monovalent
cation, E is a trivalent cation, Me and M are each independently a
trivalent cation, a tetravalent cation, a pentavalent cation, or a
hexavalent cation, X comprises O, a pentavalent anion, a hexavalent
anion, a heptavalent anion, or a combination thereof, and
0<x+2y.ltoreq.3, 0<y.ltoreq.0.5, 0.ltoreq.z<2, and
0<d.ltoreq.2.
14. An anode comprising the composite of claim 1.
15. The anode of claim 14, further comprising an additional anode
active material.
16. A lithium secondary battery comprising the anode of claim
14.
17. A method of preparing the composite of claim 1, the method
comprising: mixing a metal particle and a garnet-type lithium ion
conductor to form a first mixture; milling the first mixture;
mixing the milled first mixture with a carbon-containing material
to form a second mixture; and milling the second mixture to
preparing the composite.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the priority to and benefit of
Korean Patent Application No. 10-2015-0081503, filed on Jun. 9,
2015, in the Korean Intellectual Property Office, and all the
benefits accruing therefrom under 35 U.S.C. .sctn.119, the content
of which is incorporated herein in its entirety by reference.
BACKGROUND
[0002] 1. Field
[0003] This disclosure relates to a composite for an anode active
material, an anode including the composite, a lithium secondary
battery including the anode, and a method of preparing the
composite.
[0004] 2. Description of the Related Art
[0005] High capacity silicon-based anode materials are receiving
much attention as anode materials for next generation lithium
batteries because silicon can theoretically provide a specific
capacity of about 4,200 mAh/g. However, such anode materials
undergo a volume expansion of about 300% or greater during lithium
intercalation and deintercalation processes. Such a high volume
expansion causes cracking and pulverization of the anode materials.
Accordingly, an electrical short and continuous electrolyte
decomposition occur, resulting degraded charge and discharge
characteristics, e.g., initial charge and discharge efficiencies,
average charge and discharge efficiencies, lifespan
characteristics, and high rate discharge characteristics. These
problems have impeded commercialization of the anode materials,
despite their high theoretical capacity. Thus there remains a need
for an improved anode material.
SUMMARY
[0006] An embodiment includes a composite of an anode active
material, the composite including a metal particle, a carbon-based
material, and a garnet-type lithium ion conductor.
[0007] An embodiment includes an anode including the composite.
[0008] An embodiment includes a lithium secondary battery including
the anode.
[0009] An embodiment includes a method of preparing the
composite.
[0010] Additional aspects will be set forth in part in the
description which follows and, in part, will be apparent from the
description, or may be learned by practice of the presented
embodiments.
[0011] According to an embodiment, a composite for an anode active
material includes: a metal particle; a carbon-containing material;
and a garnet-type lithium ion conductor, wherein am amount of the
garnet-type lithium ion conductor may be greater than 1 part by
weight and less than 5 parts by weight, based on 100 parts by
weight of a total weight of the metal particle, the
carbon-containing material, and the garnet-type lithium ion
conductor.
[0012] The metal particle may include silicon (Si), tin (Sn),
germanium (Ge), aluminum (Al), an alloy of two or more of Si, Sn,
Ge, and Al, or a combination thereof.
[0013] The carbon-based material may include a carbon nanotube
(CNT), a carbon nanofiber, graphene, graphite, or a combination
thereof.
[0014] An amount of the metal particle may be in a range of about
10 parts to about 90 parts by weight, based on 100 parts by weight
of the carbon-based material.
[0015] According to an embodiment, an anode includes the composite
anode active material.
[0016] The anode may further include an additional anode active
material.
[0017] According to an embodiment, a lithium secondary battery
includes the anode.
[0018] According to one or more exemplary embodiments, a method of
preparing a composite for an anode active material includes: mixing
a metal particle and a garnet-type lithium ion conductor to form a
first mixture; milling the first mixture; mixing the milled first
mixture with a carbon-containing material to form a second mixture;
and milling the second mixture to preparing the composite.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] These and/or other aspects will become apparent and more
readily appreciated from the following description of the
embodiments, taken in conjunction with the accompanying drawings in
which:
[0020] FIG. 1 is a diagram schematically illustrating a composite
for an anode active material according to an exemplary
embodiment;
[0021] FIG. 2 is a diagram illustrating a method of preparing the
composite anode active material according to an exemplary
embodiment;
[0022] FIG. 3 is a schematic diagram schematically illustrating a
structure of a lithium secondary battery according to an exemplary
embodiment;
[0023] FIG. 4 is a graph of intensity (arbitrary units) versus
diffraction angle (28, degrees) which shows the results of X-ray
diffraction (XRD) analysis of the composites anode active materials
prepared in Example 1 and Comparative Examples 1 to 3 according to
an exemplary embodiment;
[0024] FIG. 5 is a scanning electron microscope (SEM) image of the
composite prepared in Example 1 according to an exemplary
embodiment;
[0025] FIG. 6 is an SEM image of the composite prepared in
Comparative Example 1;
[0026] FIG. 7 is an image obtained by performing energy dispersive
X-ray spectrometry (EDS) mapping on the composite prepared in
Example 1 according to an exemplary embodiment;
[0027] FIG. 8 is a graph of capacity retention (percent, %) versus
number of cycles showing changes in capacity retention and
coulombic efficiency with respect to a number of charge-discharge
cycles of coin-type half cells prepared in Example 1 and
Comparative Examples 1 to 3; and
[0028] FIG. 9 is a graph of capacity retention (percent, %) versus
number of cycles showing changes in capacity retention and
coulombic efficiency with respect to a number of charge-discharge
cycles of coin-type half cells prepared in Example 1 and
Comparative Examples 1 to 3.
DETAILED DESCRIPTION
[0029] Reference will now be made in detail to embodiments,
examples of which are illustrated in the accompanying drawings,
wherein like reference numerals refer to like elements throughout.
In this regard, the present embodiments may have different forms
and should not be construed as being limited to the descriptions
set forth herein. Accordingly, the exemplary embodiments are merely
described below, by referring to the figures, to explain aspects of
the present description. As used herein, the term "and/or" includes
any and all combinations of one or more of the associated listed
item. "Or" means "and/or." Expressions such as "at least one of,"
when preceding a list of elements, modify the entire list of
elements and do not modify the individual elements of the list.
[0030] It will be understood that when an element is referred to as
being "on" another element, it can be directly on the other element
or intervening elements may be present therebetween. In contrast,
when an element is referred to as being "directly on" another
element, there are no intervening elements present.
[0031] It will be understood that, although the terms "first,"
"second," "third," etc. may be used herein to describe various
elements, components, regions, layers, and/or sections, these
elements, components, regions, layers, and/or sections should not
be limited by these terms. These terms are only used to distinguish
one element, component, region, layer, or section from another
element, component, region, layer, or section. Thus, "a first
element," "component," "region," "layer," or "section" discussed
below could be termed a second element, component, region, layer,
or section without departing from the teachings herein.
[0032] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting. As
used herein, the singular forms "a," "an," and "the" are intended
to include the plural forms, including "at least one," unless the
content clearly indicates otherwise. "At least one" is not to be
construed as limiting "a" or "an." It will be further understood
that the terms "comprises" and/or "comprising," or "includes"
and/or "including" when used in this specification, specify the
presence of stated features, regions, integers, steps, operations,
elements, and/or components, but do not preclude the presence or
addition of one or more other features, regions, integers, steps,
operations, elements, components, and/or groups thereof.
[0033] Spatially relative terms, such as "beneath," "below,"
"lower," "above," "upper" and the like, may be used herein for ease
of description to describe one element or feature's relationship to
another element(s) or feature(s) as illustrated in the figures. It
will be understood that the spatially relative terms are intended
to encompass different orientations of the device in use or
operation in addition to the orientation depicted in the figures.
For example, if the device in the figures is turned over, elements
described as "below" or "beneath" other elements or features would
then be oriented "above" the other elements or features. Thus, the
exemplary term "below" can encompass both an orientation of above
and below. The device may be otherwise oriented (rotated 90 degrees
or at other orientations) and the spatially relative descriptors
used herein interpreted accordingly.
[0034] "About" or "approximately" as used herein is inclusive of
the stated value and means within an acceptable range of deviation
for the particular value as determined by one of ordinary skill in
the art, considering the measurement in question and the error
associated with measurement of the particular quantity (i.e., the
limitations of the measurement system). For example, "about" can
mean within one or more standard deviations, or within .+-.30%,
20%, 10% or 5% of the stated value.
[0035] Unless otherwise defined, all terms (including technical and
scientific terms) used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which this
disclosure belongs. It will be further understood that terms, such
as those defined in commonly used dictionaries, should be
interpreted as having a meaning that is consistent with their
meaning in the context of the relevant art and the present
disclosure, and will not be interpreted in an idealized or overly
formal sense unless expressly so defined herein.
[0036] Exemplary embodiments are described herein with reference to
cross section illustrations that are schematic illustrations of
idealized embodiments. As such, variations from the shapes of the
illustrations as a result, for example, of manufacturing techniques
and/or tolerances, are to be expected. Thus, embodiments described
herein should not be construed as limited to the particular shapes
of regions as illustrated herein but are to include deviations in
shapes that result, for example, from manufacturing. For example, a
region illustrated or described as flat may, typically, have rough
and/or nonlinear features. Moreover, sharp angles that are
illustrated may be rounded. Thus, the regions illustrated in the
figures are schematic in nature and their shapes are not intended
to illustrate the precise shape of a region and are not intended to
limit the scope of the present claims.
[0037] To overcome the shortcomings of silicon anode materials,
research is being conducted on which shapes and structures of
silicon are preferred to develop materials that exhibit improved
capacity and improved charge and discharge characteristics.
Introduction of porous silicon particles and use of silicon
nanostructures, such as silicon nanowires or nanotubes, to prevent
deterioration of battery characteristics caused by the volume
expansion of the silicon anode materials has been considered.
However, such techniques of controlling the nanostructure of the
silicon can use expensive process technology, such as a
high-temperature vacuum chemical vapor deposition (CVD) process, or
a process using a sacrificial template, or a chemical etching
process, resulting in difficulties in commercialization. In
addition, the large specific surface area of nano-sized particles
has significant adverse effects on the thermal stability of
batteries, and resulting in additional difficulties in the
commercialization of the silicon anode materials.
[0038] For example, a method of preparing a three-dimensional (3D)
porous silicon has been attempted, the method including forming a
plurality of pores in bulk silicon by depositing a plurality of
silver particles onto the bulk silicon and chemically etching. The
plurality of pores formed may serve to decrease a total expansion
coefficient of the silicon. However, the method of preparing the 3D
porous silicon uses a high-cost noble metal catalyst and the porous
silicon does not have a high porosity, and thus desired effects are
not sufficiently obtained therefrom.
[0039] As another example, a method of preparing a double-walled
silicon nanotube (DWSINT) has been attempted, the method including
forming a carbon-based coating layer on an outer wall of a silicon
nanotube. The coating layer formed in the method may serve to
suppress expansion of silicon. However, special equipment for a
chemical vapor deposition (CVD) process or the like is used to
perform the method of preparing the DWSINT, resulting in
difficulties in their commercialization.
[0040] Hereinafter, a composite for an anode active material
according to an exemplary embodiment, a method of preparing the
composite, an anode including the composite, and a lithium
secondary battery including the composite are disclosed in further
detail.
[0041] The composite according to an exemplary embodiment may
include a metal particle, a carbon-based material, and a
garnet-type lithium ion conductor.
[0042] An amount of the garnet-type lithium ion conductor may be
greater than 1 part by weight and less than 5 parts by weight, or
about 1.5 parts by weight to about 4 parts by weight, or about 2
parts by weight to about 3 parts by weight, based on 100 parts by
weight of the total amount of the metal particle, the carbon-based
material, and the garnet-type lithium ion conductor.
[0043] When the amount of the garnet-type lithium ion conductor is
not within the above-described range, the lithium secondary battery
including the anode that includes the composite may have a low
initial charge and discharge efficiency and degraded lifespan
characteristics.
[0044] As used herein, the term `composite` refers to a material
formed by combining two or more materials having different physical
or chemical properties than each other, wherein the composite has
properties different from individual materials constituting the
composite, and wherein the individual materials are macroscopically
or microscopically separated and distinguishable from each other in
a finished structure of the composite.
[0045] The metal particle may serve to carry out intercalation and
deintercalation of lithium ions.
[0046] The metal particle may comprise silicon (Si), tin (Sn),
germanium (Ge), aluminum (Al), or a combination thereof, or an
alloy comprising Si, Sn, Ge, Al, or a combination thereof. A
combination comprising at least one of the foregoing may be
used.
[0047] An amount of the metal particle may be in a range of about
10 parts by weight to about 90 parts by weight, about 50 parts by
weight to about 88 parts by weight, or about 60 parts by weight to
about 86 parts by weight, based on 100 parts by weight of the
carbon-based material. When the amount of the metal particle is
within the above-described range, the anode including the composite
may have a sufficiently high capacity and a volume expansion of the
metal particle may be somewhat suppressed during charging of the
lithium secondary battery including the anode. For example, the
amount of the metal particle may be in a range of about 65 parts by
weight to about 70 parts by weight, based on 100 parts by weight of
the carbon-based material.
[0048] While not wanting to be bound by theory, the carbon-based
material may carry out intercalation and deintercalation of the
lithium ions, and also to improve electrical conductivity of the
anode including the composite. In addition, during charging of the
lithium secondary battery including the anode that includes the
composite, the carbon-based material may suppress volume expansion
of the metal particle, and thus, after a number of charge and
discharge cycles, the carbon-based material may prevent the metal
particle from being pulverized. Thus, the carbon-based material may
improve lifespan characteristics of the anode including the
composite and the lithium secondary battery including the
anode.
[0049] In addition, the carbon-based material may provide an
improved electrical path in the composite such that components of
the composite may maintain electrical contact therebetween. As
such, the carbon-based material may provide the electrical path
that is connected without disconnection in the composite. In this
regard, even in a case where a part of the composite is degraded,
the carbon-based material may prevent the degraded part from being
electrically isolated. As a result, the anode may have improved
electrochemical characteristics because a structure of the
composite is stabilized. Thus, the anode and the lithium secondary
battery including the anode may have improved durability.
[0050] The carbon-based material may include a carbon nanotube
(CNT), a carbon nanofiber, graphene, graphite, or a combination
thereof.
[0051] The garnet-type lithium ion conductor may improve an ionic
conductivity of the anode including the composite. In addition,
during charging of the lithium secondary battery including the
anode that includes the composite, the garnet-type lithium ion
conductor may suppress volume expansion of the metal particle, and
thus, after a number of charge and discharge cycles, the
garnet-type lithium ion conductor may prevent the metal particle
from being pulverized. Thus, the garnet-type lithium ion conductor
may improve lifespan characteristics of the anode including the
composite and the lithium secondary battery including the
anode.
[0052] The garnet-type lithium ion conductor may be represented by
Formula 1A below:
L.sub.5+xE.sub.3Me.sub.zM.sub.2-zX.sub.d Formula 1A
[0053] In Formula 1A, L may be at least one of a monovalent cation
and a divalent cation, and a part or all of L is lithium (Li); E
may be a trivalent cation; Me and M may each independently be a
trivalent cation, a tetravalent cation, a pentavalent cation, or a
hexavalent cation; 0<x.ltoreq.3, 0.ltoreq.z<2, and
0<d.ltoreq.2; and X may comprise O, a pentavalent anion, a
hexavalent anion, a heptavalent anion, or a combination
thereof.
[0054] In Formula 1A, when x satisfies 0<x.ltoreq.2.5, E may be
lanthanum (La), and M may be zirconium (Zr).
[0055] In Formula 1A, at least a part of E may be substituted with
a Group 1 element having an atomic weight of at least 10 to provide
a composite represented by Formula 1B.
L.sub.5+xE.sub.3-aQ.sub.aMe.sub.zM.sub.2-zX.sub.d Formula 1B
wherein, in Formula 1B, L is a monovalent cation, a divalent
cation, or a combination thereof and comprises lithium, E is a
trivalent cation, Q is a Group 1 element having an atomic weight of
at least 10, Me and M are each independently a trivalent cation, a
tetravalent cation, a pentavalent cation, or a hexavalent cation, X
comprises O, a pentavalent anion, a hexavalent anion, a heptavalent
anion, or a combination thereof, 0<x.ltoreq.3, 0.ltoreq.z<2,
0<d.ltoreq.2, and 0<a.ltoreq.3.
[0056] Accordingly, the Group 1 element having an atomic weight of
at least 10 may be present within a crystalline structure of the
garnet-type oxide, e.g., to provide a garnet-type lithium ion
conductor.
[0057] The Group 1 element having an atomic weight of at least 10
may be present at a grain boundary of the garnet-type oxide to
provide the garnet-type lithium ion conductor of Formula 1B.
[0058] An amount of the Group 1 element having an atomic weight of
at least 10 may be in a range of about 0.25 part by weight to about
3.85 parts by weight, e.g., about 0.5 part by weight to about 2.0
parts by weight, or about 0.75 part by weight to about 3 parts by
weight, based on 100 parts by weight of the total amount of the
garnet-type lithium ion conductor.
[0059] The garnet-type lithium ion conductor may include a
garnet-type oxide represented by Formula 2 below:
L.sub.5+x+2yD.sub.yE.sub.3-yMe.sub.zM.sub.2-zX.sub.d Formula 2
[0060] In Formula 2, L may be at least one of a monovalent cation
and a divalent cation, and a part or all of L is Li; D may be a
monovalent cation; E may be a trivalent cation; Me and M may each
independently be a trivalent cation, a tetravalent cation, a
pentavalent cation, or a hexavalent cation; 0<x+2y.ltoreq.3,
0<y.ltoreq.0.5, 0.ltoreq.z<2, and 0<d.ltoreq.2; and X may
comprise O, a pentavalent anion, a hexavalent anion, a heptavalent
anion, or a combination thereof.
[0061] In Formula 2, when x and y may satisfy 0<x+2y.ltoreq.2.5,
E may be La, and M may be Zr.
[0062] In the garnet-type oxide of Formula 2, at least a part of
the trivalent cations present at a dodecahedral site may be
substituted with a monovalent cation having a larger ionic radius
than that of the trivalent cation. Such substitution in the
garnet-type oxide of Formula 2 provides an increased lattice
constant and reduced activation energy.
[0063] In addition, in the garnet-type oxide of Formula 2, at least
a part of the trivalent cations present at a dodecahedral site may
be substituted with a monovalent cation having a smaller
electronegativity than that of the trivalent cation, and thus a
distance between oxygen ions in the vicinity of lithium ions
present at a tetrahedral site and/or an octahedral site may vary.
As a result, migration of the lithium ions may be facilitated.
[0064] The garnet-type oxide of Formula 2 may be represented by
Formula 3 below:
L.sub.5+x+2yD.sub.yLa.sub.3-yMe.sub.zZr.sub.2-zX.sub.d Formula
3
[0065] In Formula 3, L may be at least one of a monovalent cation
and a divalent cation, and a part or all of L is Li; D may be a
monovalent cation; Me may be a trivalent cation, a tetravalent
cation, a pentavalent cation, or a hexavalent cation;
0<x+2y.ltoreq.3, 0<y.ltoreq.0.5, 0.ltoreq.z<2, and
0<d.ltoreq.2; and X may be 0, a pentavalent anion, a hexavalent
anion, a heptavalent anion, or a combination thereof. In an
exemplary embodiment, x and y in Formula 3 may satisfy
0<x+2y.ltoreq.1. In another exemplary embodiment, x and y in
Formula 3 may satisfy 1<x+2y.ltoreq.2. In another exemplary
embodiment, x and y in Formula 3 may satisfy
2<x+2y.ltoreq.2.5.
[0066] The garnet-type oxide of Formula 2 may be represented by
Formula 4 below:
Li.sub.5+x+2yD.sub.yLa.sub.3-yZr.sub.2X.sub.d Formula 4
[0067] In Formula 4, D may be potassium (K), rubidium (Rb), or
cesium (Cs); 0<x+2y.ltoreq.3, 0<y.ltoreq.0.5, and
0<d.ltoreq.2; and X may be 0, a pentavalent anion, a hexavalent
anion, a heptavalent anion, or a combination thereof.
[0068] In Formula 4, x and y may satisfy 2<x+2y.ltoreq.3.
[0069] When the monovalent cation, which substitutes for the
trivalent cation of the garnet-type oxides of Formulae 1 to 4, has
a larger ionic radius than that of the trivalent cation, the
migration of the lithium ions may be more facilitated.
[0070] D in Formulae 1 to 4 may be K, Rb, Cs, or a combination
thereof.
[0071] Me in Formulae 1 to 4 may be a transition metal, For
example, Me in Formulae 1 to 4 may include tantalum (Ta), niobium
(Nb), yttrium (Y), scandium (Sc), tungsten (W), molybdenum (Mo),
antimony (Sb), bismuth (Bi), hafnium (Hf), vanadium (V), germanium
(Ge), silicon (Si), aluminum (Al), gallium (Ga), titanium (Ti),
cobalt (Co), indium (In), zinc (Zn), chromium (Cr), or a
combination thereof.
[0072] L in Formulae 1 to 4 may include lithium (Li), sodium (Na),
magnesium (Mg), calcium (Ca), potassium (K), hydrogen (H), or a
combination thereof. For example, L in Formulae 1 to 4 may include
a Li ion, and optionally, a monovalent and/or divalent ion, such as
Na and Mg.
[0073] The garnet-type oxides of Formulae 1 to 4 may have an ionic
conductivity of at least about 3.times.10.sup.-4 siemens per
centimeter (S/cm) at a temperature of 25.degree. C. For example,
the garnet-type oxides of Formulae 1 to 4 may have an ionic
conductivity of at least about 6.times.10.sup.-4 S/cm, at least
about 6.5.times.10.sup.-4 S/cm, at least about 7.times.10.sup.-4
S/cm, at least about 7.5.times.10.sup.-4 S/cm, at least about
8.times.10.sup.-4 S/cm, or at least about 8.3.times.10.sup.-4 S/cm,
at a temperature of 25.degree. C.
[0074] The garnet-type oxides of Formulae 1 to 4 may have an
activation energy in a range of less than about 0.34 electron volts
(eV) at a temperature in a range of about -10.degree. C. to about
100.degree. C. For example, the garnet-type oxides of Formulae 1 to
4 may have an activation energy of about 0.30 eV or less or about
0.29 eV or less, at a temperature in a range of about -10.degree.
C. to about 100.degree. C. As the activation energy decreases, the
ionic conductivity of each of the garnet-type oxides according to a
temperature becomes insensitive to temperature, and thus, the
garnet-type oxides of Formulae 1 to 4 may have improved
low-temperature characteristics.
[0075] Hereinafter, a method of preparing the garnet-type lithium
ion conductor will be disclosed in further detail.
[0076] The method of preparing the garnet-type lithium ion
conductor may include: forming a precursor mixture by mixing
precursors of the garnet-type lithium ion conductor and milling the
resultant; and sintering the precursor mixture in an air atmosphere
at a temperature of about 800.degree. C. to about 1,250.degree. C.
for about 2 hours to about 40 hours. For example, the method of
preparing the composite may comprise mixing the metal particle and
the garnet-type lithium ion conductor to form a first mixture;
milling the first mixture; mixing the milled first mixture with a
carbon-containing material to form a second mixture; and milling
the second mixture to preparing the composite.
[0077] Any suitable precursor including a metal of the garnet-type
lithium ion conductor and available in the art may be used as the
precursor of the garnet-type lithium ion conductor.
[0078] The sintering of the precursor mixture may be performed at a
temperature of about 900.degree. C. to about 1,200.degree. C.,
about 950.degree. C. to about 1,150.degree. C., or about
1000.degree. C. to about 1,100.degree. C. for about 5 hours to
about 30 hours, about 7 hours to about 25 hours, or about 9 hours
to about 20 hours.
[0079] When the temperature at which the sintering is performed is
too low, reactive sintering may be insufficient. However, when the
temperature at which the sintering is performed is too high,
lithium may be subjected to phase decomposition or volatilization.
In addition, when the time for which the sintering is performed is
too short, reactive sintering may be insufficient. However, when
the time for which the sintering is performed is too long, lithium
may volatilize.
[0080] The method of preparing the garnet-type lithium ion
conductor may further include: preliminarily sintering the
precursor mixture at a relatively low temperature, before the
sintering of the precursor mixture. The preliminarily sintering of
the precursor mixture may be performed twice or more times, e.g., 2
to 10 times.
[0081] The method of preparing the garnet-type lithium ion
conductor may further include: milling the sintered resultant
products after the sintering of the precursor mixture.
[0082] The milling may be each performed using any suitable mill,
such as a ball mill. For example, the milling may be each performed
using a spex mill or a planetary mill.
[0083] The garnet-type lithium ion conductor obtained according to
the above-described method may have various forms, such as powder,
a thin film, or a pellet, and the form thereof may be appropriately
selected according to the use thereof.
[0084] FIG. 1 is a diagram schematically illustrating a composite
for an anode active material 1 according to an exemplary
embodiment.
[0085] Referring to FIG. 1, the composite 1 may include a metal
particle 10, a garnet-type lithium ion conductor 11, and a
carbon-based material 12.
[0086] The garnet-type lithium ion conductor 11 and the
carbon-based material 12 may be disposed on a surface of the metal
particle 10 and/or may be disposed close to the surface.
[0087] Hereinafter, a method of preparing the composite anode
active material according to an exemplary embodiment will be
disclosed in further detail.
[0088] FIG. 2 is a diagram illustrating a method of preparing the
composite anode active material according to an exemplary
embodiment.
[0089] Referring to FIG. 2, the method of preparing the composite
includes: performing a first step of mixing the metal particles 10
with the garnet-type lithium ion conductors (LLZ) 11 to form a
first mixture and milling the first mixture; and performing a
second step of mixing the milled first mixture, e.g., a precursor
1' of a composite for an anode active material with carbon-based
materials (e.g., CNTs) 12 to form a second mixture and milling the
second mixture.
[0090] According to the milling of the first step, the precursor 1'
including the metal particles 10 and the garnet-type lithium ion
conductors 11 disposed on at least a surface of the metal particles
10 may be obtained.
[0091] According to the milling of the second step, a composite 1
for an anode active material may be obtained, the composite 1
including the metal particles 10 and the garnet-type lithium ion
conductor 11 and the carbon-based material 12, which are formed on
at least a surface of the metal particles 10.
[0092] Each of the milling of the first step and the milling of the
second step may be performed for about 120 minutes or less, for
example, about 60 minutes or less, 10 minutes or less, or for about
1 minute to about 120 minutes, or about 1 minute to about 8
minutes.
[0093] An apparatus used for the milling process is not
particularly limited, and any suitable apparatus available in the
art may be used. For example, the milling process may be performed
using a spex mill or a planetary mill.
[0094] Each of the milling of the first step and the milling of the
second step may be performed according to, other than the dry
milling as described above, a wet milling using a medium.
[0095] Before performing each of the milling of the first step and
the milling of the second step, at least one of the metal particle
10, the garnet-type lithium ion conductor (LLZ) 11, the precursor
1' of a composite anode active material, and the carbon-based
material (e.g., CNT) 12 may be added to a medium to be subjected to
sonification or a stirring process. Following the sonification or
stirring process, the medium may be removed, and then the milling
described above may be performed. Following the sonification or
stirring process, the composite 1 anode active material having
improved dispersity of the garnet-type lithium ion conductor 11 and
the carbon-based material 12 may be finally obtained.
[0096] The medium may comprise an alcohol (e.g., a C1 to C20
alcohol such as ethanol), acetone, water, N-methyl-2-pyrrolidone
(NMP), toluene, tetrahydrofuran (THF), hexane, or a combination
thereof.
[0097] Hereinafter, an anode according to an exemplary embodiment
will be disclosed in further detail.
[0098] The anode may include the composite anode active material
described above.
[0099] The anode may further include an additional anode active
material that is suitable for use in a lithium secondary battery in
addition to the composite anode active material.
[0100] The additional anode active material may include a
carbon-based material capable of intercalating or deintercalating
lithium ions, such as graphite (which may be identical to or
different from the graphite that can be used as the carbon-based
material included in the composite anode active material) or
carbon; a lithium metal; an alloy of the lithium metal; or a
silicon oxide-based material. A combination comprising at least one
of the foregoing may be used.
[0101] The anode may further include a binder and/or a conductive
agent in addition to the composite anode active material and the
additional anode active material, if present.
[0102] The binder may facilitate adherence between components such
as the composite anode active material, the additional anode active
material, and the conductive agent, and adherence of the anode to a
current collector. Examples of the binder include polyacrylic acid
(PAA), polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl
cellulose (CMC), starch, hydroxypropyl cellulose, regenerated
cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene,
polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated
EPDM, styrene-butadiene-rubber, fluorinated rubber, a copolymer
thereof, or a combination thereof.
[0103] The binder may include lithium ions.
[0104] The amount of the binder may be in a range of about 1 part
by weight to about 20 parts by weight, for example, in a range of
about 2 parts by weight to about 7 parts by weight, based on 100
parts by weight of the total amounts of the composite anode active
material and the additional anode active material. When the amount
of the binder is within the range above, e.g., about 1 part by
weight to about 20 parts by weight, the adherence of the anode to
the current collector may be suitably strong.
[0105] The conductive agent is not particularly limited as long as
the conductive agent has suitable conductivity and does not induce
an undesirable chemical change in the lithium secondary battery
including the conductive agent.
[0106] The conductive agent may include a carbonaceous conductive
agent selected from carbon black, carbon fiber, and graphite (which
may be identical to or different from the graphite that can be used
as the carbon-based material included in the composite anode active
material), or a combination thereof. The carbon black may be, for
example, selected from acetylene black, Ketjen black, Super P
carbon, channel black, furnace black, lamp black, thermal black, or
a combination thereof. The graphite may include natural graphite,
artificial graphite, or a combination thereof.
[0107] The anode may further include, an additional conductive
agent other than the carbonaceous conductive agent described
above.
[0108] The additional conductive agent may be selected from a
conductive fiber, such as a metal fiber; a metal powder such as a
fluorinated carbon powder, an aluminum powder, or a nickel powder;
a conductive whisker such as a zinc oxide or a potassium titanate;
a polyphenylene derivative; or a combination thereof.
[0109] The amount of the conductive agent may be in a range of
about 0.5 part by weight to about 10 parts by weight, for example,
in a range of about 0.01 part by weight to about 5 parts by weight,
based on 100 parts by weight of the total amounts of the composite
anode active material and additional anode active material. When
amount of the conductive agent is within the range above, e.g.,
about 0.5 part by weight to about 10 parts by weight, an anode
having improved ion conductivity may be finally obtained.
[0110] The anode may be, for example, prepared as follows.
[0111] First, the composite anode active material, the additional
anode active material, the binder, a solvent, the carbonaceous
conductive agent, and/or the additional conductive agent are mixed
to prepare a composition for forming an anode active material
layer.
[0112] Thereafter, the composition for forming the anode active
material layer may be coated on an anode current collector, and
then, dried to prepare an anode.
[0113] The anode current collector may have a thickness in a range
of about 3 micrometers (.mu.m) to about 500 .mu.m. The anode
current collector is not particularly limited as long as the
current collector has sufficient conductivity and does not induce
an undesirable chemical change in the lithium secondary battery
including the anode current collector. For example, the anode
current collector may include copper; stainless steel; aluminum;
nickel; titanium; heat treated carbon; copper or stainless steel
surface-treated with carbon, nickel, titanium or silver; or an
aluminum-cadmium alloy. A combination comprising at least one of
the foregoing may be used. Also, as in an embodiment including a
cathode current collector which will be further described below,
the surface of the anode current collector may be roughened, e.g.,
to include a minute concavity and convexity on the surface of the
anode current collector to improve adherence of the anode active
material to the anode current collector. The anode current
collector may be used in any suitable form, such as a film, a
sheet, a foil, a net, a porous body, a foaming body, a non-woven
fabric, or a combination thereof.
[0114] The solvent may include N-methyl pyrrolidone (NMP), acetone,
water, or a combination thereof. An amount of the solvent may be in
a range of about 1 part by weight to about 50 parts by weight,
based on 100 parts by weight of the anode active material. When the
amount of the solvent is within the range above, formation of the
active material layer may be facilitated.
[0115] A lithium secondary battery according to an exemplary
embodiment includes the anode.
[0116] FIG. 3 is a schematic diagram illustrating a structure of a
lithium secondary battery 20 according to an exemplary embodiment
of the present inventive concept.
[0117] Referring to FIG. 3, the lithium secondary battery 20
includes a cathode 23, an anode 21, and a separator 22.
[0118] The cathode 23, the anode 21, and the separator 22 may be
wound or folded and disposed in a battery case 24. Subsequently, an
electrolyte (not shown) is injected into the battery case 24, and
the battery case 24 is sealed by a cap assembly 25, thereby
completing the preparation of the lithium secondary battery 20. The
battery case 24 may be a coin, rectangular, or thin-film type. For
example, the lithium secondary battery 20 may be a large
thin-film-type battery.
[0119] The lithium secondary battery 20 may have improved initial
charge and discharge efficiency and lifespan.
[0120] Hereinafter, a method of preparing the lithium secondary
battery will be described in further detail.
[0121] First, an anode is prepared by the method described
above.
[0122] Thereafter, a cathode is prepared using a method similar to
the method of preparing the anode. For example, a lithium
transition metal oxide, a binder, a conductive agent, and a solvent
may be mixed to prepare a composition for forming a cathode active
material layer. Subsequently, the composition for forming the
cathode active material layer may be coated on the cathode current
collector, and then, dried to prepare a cathode.
[0123] The types and the amounts of the binder, the conductive
agent, and the solvent used to prepare the composition for forming
the cathode active material layer may be the same as those for
preparing the composition for forming the anode active material
layer.
[0124] The anode active material may include LiCoO.sub.2,
LiNiO.sub.2, LiMnO.sub.2, LiMn.sub.2O.sub.4,
Li(Ni.sub.aCo.sub.bMn.sub.c)O.sub.2 (wherein 0<a<1,
0<b<1, 0<c<1, and a+b+c=1),
LiNi.sub.1-yCo.sub.yO.sub.2, LiCo.sub.1-yMn.sub.yO.sub.2, Li
Ni.sub.1-yMn.sub.yO.sub.2 (wherein 0.ltoreq.Y<1),
LiMn.sub.2-zNi.sub.3O.sub.4, LiMn.sub.2-zCo.sub.zO.sub.4 (wherein
0<Z<2), LiCoPO.sub.4, LiFePO.sub.4, or a combination
thereof.
[0125] The cathode current collector may have a thickness in a
range of about 3 .mu.m to about 500 .mu.m. The cathode current
collector is not particularly limited as long as the current
collector has sufficient conductivity and does not induce an
undesirable chemical change in the lithium secondary battery
including the cathode current collector. For example, the cathode
current collector may include stainless steel; aluminum; nickel;
titanium; heat treated carbon; aluminum or stainless steel
surface-treated with carbon, nickel, titanium, or silver; or a
combination thereof. Also, a surface roughness including a minute
concavity and convexity may be formed on the surface of the cathode
current collector to improve adherence of the cathode active
material to the cathode current collector, and the cathode current
collector may be used in various forms such as a film, a sheet, a
foil, a net, a porous body, a foaming body, or a non-woven
fabric.
[0126] The lithium secondary battery may be prepared by disposing a
separator between the cathode and the anode and supplying an
organic liquid electrolyte thereto.
[0127] The lithium secondary battery may be prepared by, for
example, sequentially stacking the anode, the separator, and the
cathode; winding or folding the stacked structure, then enclosing
the wound or folded structure in a coin or rectangular type battery
case or a pouch; and then disposing, e.g., injecting, the organic
liquid electrolyte into the battery case or the pouch to
manufacture the lithium secondary battery.
[0128] The separator can be porous, and a diameter of a pore of the
separator may be in a range of about 0.01 .mu.m to about 10 .mu.m,
and a thickness of the separator may be in a range of about 5 .mu.m
to about 300 .mu.m. In greater detail, the separator may be a sheet
or a non-woven fabric made of olefin-based polymer such as
polypropylene or polyethylene; or a glass fiber.
[0129] The organic liquid electrolyte may be prepared by dissolving
a lithium salt in an organic solvent.
[0130] The organic solvent may comprise propylene carbonate,
ethylene carbonate, fluoroethylene carbonate, butylene carbonate,
dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate,
methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl
carbonate, dipropyl carbonate, dibutyl carbonate, benzonitrile,
acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran,
.gamma.-butyrolactone, dioxolane, 4-methyldioxolan,
N,N-dimethylformamide, dimethylacetamide, dimethylsulfoxide,
dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane,
chlorobenzene, nitrobenzene, diethylene glycol, dimethylether, or a
combination thereof.
[0131] The lithium salt may comprise LiPF.sub.6, LiBF.sub.4,
LiSbF.sub.6, LiAsF.sub.6, LiClO.sub.4, LiCF.sub.3SO.sub.3,
Li(CF.sub.3SO.sub.2).sub.2N, LiC.sub.4F.sub.9SO.sub.3, LiAlO.sub.2,
LiAlCl.sub.4,
LiN(C.sub.xF.sub.2x+1SO.sub.2)(C.sub.yF.sub.2y+1SO.sub.2) (wherein
x and y are natural numbers), LiCl, LiI, or a combination
thereof.
[0132] In a lithium secondary battery according to another
exemplary embodiment, an organic solid electrolyte and/or an
inorganic solid electrolyte may be used, optionally in combination
with the organic liquid electrolyte. When the organic solid
electrolyte and/or the inorganic solid electrolyte are used, the
organic solid electrolyte and/or inorganic solid electrolyte may
act as a separator in some cases, and thus, the separator may be
omitted if desired.
[0133] As the organic solid electrolyte, for example, a
polyethylene derivative, a polyethylene oxide derivative, a
polypropylene oxide derivative, a phosphoric acid ester polymer, a
polyester sulfide, polyvinyl alcohol, a polyvinylidene fluoride, or
a combination thereof may be used.
[0134] As the inorganic solid electrolyte, for example, a lithium
nitride, a lithium halogenide, or a lithium sulfide, such as
Li.sub.3N, LiI, Li.sub.5NI.sub.2, Li.sub.3N--LiI--LiOH,
Li.sub.2SiS.sub.3, Li.sub.4SiO.sub.4,
Li.sub.3PO.sub.4--Li.sub.2S--SiS.sub.2, or a combination thereof
may be used.
[0135] Hereinafter, an exemplary embodiment will now be described
in greater detail with reference to the following examples.
However, the following examples are for illustrative purposes only
and are not intended to limit the scope of the disclosure.
Examples
Preparation Example 1
Preparation of a Garnet-Type Lithium Ion Conductor
(Li.sub.7La.sub.3Zr.sub.2O.sub.12)
[0136] LiOH.H.sub.2O as an Li precursor, La.sub.2O.sub.3 as a La
precursor, and ZrO.sub.2 as a Zr precursor, which were used as
starting materials, were stoichiometrically mixed together to
obtain Li.sub.5+x+2yD.sub.yLa.sub.3-yZr.sub.2O.sub.12 where x=2 and
y=0.
[0137] The mixture was pulverized by mixing in 2-propanol using a
planetary ball mill (400 rpm, zirconia oxide balls) for 6 hours.
The pulverized mixed powder was put in an alumina crucible and
sintered in an air atmosphere at 900.degree. C. for 12 hours.
[0138] To supplement a loss amount of Li, an excess amount of LiOH
corresponding to 10 wt % of the amount of the Li, based on the
amount of Li in the composition of a final product, was used.
[0139] The mixture with LiOH added thereto was pulverized by mixing
in 2-propanol using a planetary ball mill (500 rpm, zirconia oxide
balls) for 6 hours. The sintered powder was cooled and molded in
the form of a pellet and sintered in an air atmosphere at
1,100.degree. C. for 20 hours, thereby completing the preparation
of a garnet-type lithium ion conductor.
Example 1 and Comparative Examples 1 to 3
Preparation of a Composite for an Anode Active Material, an Anode,
a Coin Half Cell, and a Coin Full Cell
Comparative Example 1
Preparation of a Composite for an Anode Active Material
[0140] Silicon nanoparticles (SiNPs) (silicon nanopowder, a product
of CN Vision Co. Ltd.) were mixed with carbon nanotubes (CTube-120,
a product of CNT Co. Ltd). Afterwards, the mixture was milled using
a mechanical milling apparatus (SPEX Mill) for about 30 minutes,
thereby obtaining a composite for an anode active material.
Example 1 and Comparative Examples 2 and 3
Preparation of a Composite for an Anode Active Material
[0141] SiNPs (silicon nanopowder, a product of CN Vision Co. Ltd.)
were mixed with the garnet-type lithium ion conductor of
Preparation Example 1. Afterwards, the mixture was milled using a
mechanical milling apparatus (SPEX Mill) for about 30 minutes,
thereby obtaining a precursor of the composite for an anode active
material. Then, the precursor of the composite anode active
material was mixed with carbon nanotubes (CTube-120, a product of
CNT Co. Ltd). Afterwards, the mixture was milled using a mechanical
milling apparatus (SPEX Mill) for about 30 minutes, thereby
obtaining a composite for an anode active material.
[0142] A ratio at which the silicon nanoparticles, the carbon
nanotubes, and the garnet-type lithium ion conductor are mixed in
each of the example and the comparative examples above are shown in
Table 1 below.
TABLE-US-00001 TABLE 1 Amounts (parts by weight) Compar- Compar-
Compar- Exam- ative ative ative Component ple 1 Example 1 Example 2
Example 3 Silicon nanoparticles 67 70 69 65 Carbon nanotubes 30 30
30 30 Garnet-type lithium ion 3 0 1 5 conductor
(Preparation of an Anode)
[0143] 20 parts by weight of each of the composite anode active
material, 80 parts by weight of graphite (MC20, a product of
Mitsubishi Chemical Co., Ltd.), and 10 parts by weight of a binder
solution (i.e., a 4 volume % Li-PAA solution prepared by dissolving
PAA (polyacrylic acid, a product of Aldrich) in water to obtain an
aqueous PAA solution and adding LiOH to the aqueous PAA solution)
were mixed together to prepare a composite for forming an anode
active material layer. Subsequently, the composition for forming
the anode active material layer was coated on a copper film, which
is an anode current collector, to have a thickness of 100 .mu.m.
The coated copper film was dried first at a temperature of
80.degree. C., dried a second time at a temperature of 120.degree.
C. in a vacuum, and then the dried product was roll-pressed to
prepare an anode.
(Preparation of a Coin Half Cell)
[0144] Thereafter, the anode was rolled into a cylinder having a
diameter of 12 mm and a lithium metal was used as a counter
electrode to prepare a 2032-type coin half cell. In this regard,
the organic liquid electrolyte was a 1.3M LiPF.sub.6 solution in a
mixture of ethylene carbonate, diethylene carbonate, and
fluoroethylene carbonate at a weight ratio of 2:6:2.
(Preparation of a Coin Full Cell)
[0145] Li.sub.1.2Ni.sub.0.13Co.sub.0.13Mn.sub.0.53O.sub.2 (622 NCM)
as a cathode active material, polyvinylidene fluoride (PVDF) as a
binder, and Denka black as a conductive agent were mixed at a
weight ratio of 92:4:4 to obtain a solid-state mixture. Afterwards,
the solid-state mixture was dispersed in N-methyl-2-pyrrolidone to
obtain a composition for forming a cathode active material layer.
Subsequently, the composition for forming the cathode active
material layer was coated on an aluminum foil having a thickness of
15 .mu.m. The coated aluminum foil was dried first in an oven at a
temperature of 90.degree. C. for about 2 hours, and dried a second
time in a vacuum oven at a temperature of 120.degree. C. for about
2 hours, thereby completely evaporating the solvent. Then, the
resultant product was rolled and punched to prepare a cathode.
[0146] The cathode, the anodes of Example 1 and Comparative
Examples 1 to 3, a polyethylene separator, and a liquid electrolyte
were used to prepare 18650-type coin full cells. In this regard,
the liquid electrolyte was a solution containing 1.1M LiPF.sub.6
and 0.2M LiBF.sub.4 in a mixture of ethylene carbonate, diethylene
carbonate, and fluoroethylene carbonate at a weight ratio of
2:6:2.
Evaluation Examples
Evaluation Example 1
Analysis of an X-Ray Diffraction (XRD) Pattern of a Composite for
an Anode Active Material
[0147] The XRD patterns of the composites for an anode active
material of Example 1 and Comparative Examples 1 to 3 were each
analyzed by using a Rigaku RINT2200HF.sup.+ diffractometer with Cu
K.alpha. radiation (1.540598 .ANG.) and results obtained therefrom
are shown in FIG. 4.
[0148] Referring to FIG. 4, it was confirmed that the crystalline
structures of the composites prepared in each example were not
significantly different from each other. In this regard, it was
confirmed that the addition of the garnet-type lithium ion
conductor did not produce impurities in the composites that were
finally obtained and did not change the crystalline structures of
the final composites. That is, the addition of the garnet-type
lithium ion conductor produced the composites having satisfactory
crystallinity.
Evaluation Example 2
Analysis of a Scanning Electron Microscope (SEM) Image of a
Composite for an Anode Active Material
[0149] SEM images of the composites of Example 1 and Comparative
Example 1 are captured by a SEM-FIB device (FEI, Helios 450F1) and
are respectively shown in FIGS. 5 and 6. FIG. 5 is an SEM image of
the composite of Example 1, and FIG. 6 is an SEM image of the
composite of Comparative Example 1.
[0150] Referring to FIGS. 5 and 6, it was confirmed that the
composite of Example 1 showed more uniform particle distribution
than particle distribution of the composite of Comparative Example
1.
Evaluation Example 3
Analysis of an Energy Dispersive Spectrometer (EDS) Mapping Images
of a Composite for an Anode Active Material
[0151] An EDS mapping image of the composite of Example 1 was
captured by an energy dispersive X-ray spectrometer (Bruker, D8
Adavance), and is shown in FIG. 7.
[0152] Referring to FIG. 7, it was confirmed that the garnet-type
lithium ion conductor was included in the composite of Example 1
(based on the presence of La and Zr in the EDS mapping image).
Evaluation Example 4
Evaluation of Charge and Discharge Characteristics of a Coin Half
Cell
[0153] Charge and discharge characteristics of the coin half cells
of Example 1 Comparative Examples 1 to 3 were evaluated by using a
charger and discharger (TOYO-3100, a product of TOYO SYSTEM Co.
Ltd). In greater detail, in a first cycle (n=1), each of the coin
half cells was charged at a C-rate of 0.1 C (unit: mA/g) until a
voltage of 0.01 V was reached, and then, discharged at a rate of
0.1 C until a voltage of 1.5 V was reached. Then, each of the coin
half cells was rested for 10 minutes. Subsequently, in a second
cycle (n=2), each of the coin half cells was charged at a C-rate of
0.2 C (unit: mA/g) at room temperature (25.degree. C.) until a
voltage of 0.01 V was reached, and then, discharged at a rate of
0.2 C until a voltage of 1.5 V was reached. Then, each of the coin
half cells was rested for 10 minutes. Subsequently, in a third
cycle (n=3) or beyond (n>3), each of the coin half cells was
charged at a C-rate of 1.0 C (unit: mA/g) at room temperature
(25.degree. C.) until a voltage of 0.01 V was reached, and then,
discharged at a rate of 1.0 C until a voltage of 1.5 V was reached.
The charge and discharge cycle described above was repeated 80
times (i.e., n=80). The letter "C" denotes a discharge rate of a
cell, which is a value obtained by dividing a total capacity of the
cell by a total discharge time.
Evaluation of Initial Charge and Discharge Efficiency and Capacity
Retention
[0154] An initial charge and discharge efficiency and a capacity
retention in a 80.sup.th charge and discharge cycle of each of the
coin half cells of Example 1 and Comparative Examples 1 and 3 were
evaluated, and results obtained therefrom are shown in Table 2
below.
TABLE-US-00002 TABLE 2 Compar- Compar- Compar- Exam- ative ative
ative ple 1 Example 1 Example 2 Example 3 Initial charge and
discharge 89.5 88.5 88.0 85.2 efficiency *.sup.1(%) Capacity
retention *.sup.2 89.6 84.8 83.2 88.0 (@ 80.sup.th cycle) *.sup.1
Initial charge and discharge efficiency = (discharge capacity of
the cell in a 2.sup.nd cycle/charge capacity of the cell in the
1.sup.st cycle) .times. 100 *.sup.2 capacity retention of the
80.sup.th cycle = (discharge capacity of the cell in the 80.sup.th
cycle)/(discharge capacity of the cell in the 3.sup.rd cycle)
.times. 100
[0155] Referring to Table 2, the coin half cell of Example 1 has
improved initial charge and discharge efficiency and excellent
capacity retention in the 80.sup.th cycle compared to those of the
coin half cells of Comparative Examples 1 to 3.
Comparison of Cycle Lifespan Characteristics
[0156] Lifespan of each of the coin half cells of Example 1 and
Comparative Examples 1 to 3 was shown in FIG. 8. In FIG. 8, a
coulombic efficiency is calculated according to Equation 1
below:
Coulombic efficiency (%)=(discharge capacity of the cell in the
n.sup.th cycle)/(charge capacity of the cell in the n.sup.th
cycle).times.100% Equation 1
[0157] Referring to FIG. 8, it was confirmed that the coin half
cell of Example 1 had excellent lifespan characteristics compared
to that of the coin half cells of Comparative Examples 1 to 3.
Evaluation Example 5
Evaluation of Charge and Discharge Characteristics of a Coin Full
Cell
[0158] A charge and discharge test was performed on the coin full
cells of Example 1 and Comparative Examples 1 to 3 as follows.
[0159] First, each of the coin full cells was charged at a C-rate
of 0.1 C at a temperature of 25.degree. C. until a voltage of 4.2 V
was reached, and then, discharged at a C-rate of 0.1 C until a
voltage of 2.5 V was reached (a first cycle in a formation
process).
[0160] Then, each of the coin full cells was charged at a C-rate of
0.1 C at a temperature of 25.degree. C. until a voltage of 4.2 V
was reached, and then, discharged at a C-rate of 0.1 C until a
voltage of 2.5 V was reached (a second cycle in the formation
process). The C rate is a discharge rate of a cell, and is obtained
by dividing a total capacity of the cell by a total discharge
period of time, e.g., a C rate for a battery having a discharge
capacity of 1.6 ampere-hours would be 1.6 amperes.
[0161] Subsequently, each of the coin full cells undergone the
formation process was charged at a C-rate of 1 C at a temperature
of 25.degree. C. until a voltage of 4.2 V was reached, and then,
discharged at a C-rate of 1 C until a voltage of 2.5 V was reached.
A discharge capacity of each of the coin full cells was measured at
the point, and the measured value was recorded as the discharge
capacity in the 1.sup.st cycle. The charge and discharge cycle
described above was repeated 100 times.
[0162] A capacity retention and a coulombic efficiency of each of
the coin full cells in each cycle were calculated, and results
obtained therefrom are shown in FIG. 9. In FIG. 9, the coulombic
efficiency is calculated according to Equation 1 above. In
addition, the capacity retention in the 100.sup.th cycle is shown
in Table 3 below.
TABLE-US-00003 TABLE 3 Compar- Compar- Compar- Exam- ative ative
ative ple 1 Example 1 Example 2 Example 3 Capacity retention
*.sup.1 78.1 70.1 72.2 75.0 (@ 100.sup.th cycle) *.sup.1 capacity
retention = (discharge capacity of the cell in the 100.sup.th
cycle)/(discharge capacity of the cell in the 1.sup.st cycle)
.times. 100%
[0163] Referring to Table 3 and FIG. 9, it was confirmed that the
coin full cell of Example 1 had improved lifespan characteristics
and high capacity retention in the 100.sup.th cycle compared to
those of the coin full cells of Comparative Examples 1 to 3.
[0164] The composite anode active material according to the
exemplary embodiment may act as a support against volume expansion
of the electrodes during charging and discharging of the cells to
ease the volume expansion of the electrodes. In addition, the
composite anode active material allows lithium ions to quickly pass
therethrough to improve ion conductivity of the electrodes. In this
regard, a contact surface area between metal particles (e.g., Si)
and an electrolyte decreases, and a side reaction at an interface
is less likely to occur. Accordingly, an electrode including the
composite anode active material may have excellent lifespan
characteristics.
[0165] It should be understood that exemplary embodiments described
herein should be considered in a descriptive sense only and not for
purposes of limitation. Descriptions of features or aspects within
each exemplary embodiment should be considered as available for
other similar features or aspects in other exemplary
embodiments.
[0166] While one or more exemplary embodiments have been described
with reference to the figures, it will be understood by those of
ordinary skill in the art that various changes in form and details
may be made therein without departing from the spirit and scope as
defined by the following claims.
* * * * *